I've been there before. Like morrison, I was in a relationship like that for five years.
My advice to you, the sooner you get out the better.
You're doing more damage to yourself than you think. I just got out of that relationship about 6 months ago. I have more issues with my self confidence than ever before.
I have trust issues, where before I easily trusted people. I'm always afraid a guy is going to let me down. I'm afraid to get close to anyone. I had to push myself to finally leave the relationship. I moved back home with mom, changed my cell phone number, severed all ties with that guy. It will be hard at first, all break-ups are...but you'll get through it.
Once you finally do it, a huge weight will be lifted off your shoulders. Hope I helped. :]